By Pritha Sarkar

RIO DE JANEIRO (Reuters) - Dethroning champions China has been the number one target for Japan at the Rio Olympics but after a day of falls and botched landings in men's qualifying on Saturday, Kohei Uchimura and his teammates were left with sore bodies and bruised egos.

Uchimura suffered the most spectacular of falls from the horizontal bar -- an apparatus on which he is the world champion -- as he lost his grip following a release and catch maneuver and produced a deafening thud as he landed on his back.

The glaring errors on every apparatus barring the floor exercise meant Japan's collective score of 269.294 was surpassed by the United States' total of 270.405.

London Games bronze medalists Britain were provisionally in third place with 268.670, ahead of jubilant hosts Brazil -- who were fielding a full team in the men's Olympic competition for the first time.

Japan's woes paled into insignificance when Frenchman Samir Ait Said and German gymnast Andreas Toba provided a painful reminder of just how dangerous and cruel the sport can be.

Ait Said discovered the perils of pursuing his Olympic dreams when he suffered a broken leg that was left dangling from below his knee following a crash landing from the vault.

He was wheeled out of the arena on a stretcher shortly after Toba cried out in agony following a fall from a tumbling run on the floor exercise.

Incredibly Toba went on to perform on the pommel horse but as he limped off that apparatus with his arms around his teammates, it was clear his Rio adventure was over.

"Andreas got hurt on the floor and maybe tore his ACL, so he won't compete anymore at these Olympics," teammate Fabian Hambuechen said.

While Japan lived to fight another day, Uchimura lost his chance to be in the running for the horizontal bar gold as his score of 14.300 left him well outside the top eight scores needed to reach the apparatus final.

That mishap did not stop the Japanese heartthrob from leading the standings for the all around final, where he will be bidding to become the first gymnast since compatriot Sawao Kato in 1972 to win successive Olympic titles in the event that tests skills across six apparatus.

Japan can forget about Saturday's horror show since none of the scores will be carried through to Monday's team final but what they do know is that if they want to end China's eight-year reign as Olympic champions, they simply cannot afford another similar performance.

"What happened today can only make me stronger," Uchimura told reporters.

"I need to repress my feelings so I can perform better at the next competition."

While in qualifying, four competitors from each country compete on each apparatus, with only the top three scores counting toward the total, in the final each nation will put forward three athletes and all three scores will count.

Since 1994, Chinese men have won 10 of 12 world championship team titles and three of the five Olympic golds on offer.

But the team that were toppled from their lofty perch by Japan at last year's world championships will be eager to prove that they have recovered from the bronze medal finish in Glasgow when they compete in the day's third and final subdivision.

(Additional reporting by Liana Baker, Editing by Toby Davis and Tom Brown)